1. Field of the Invention
The present invention relates to a layered polycrystalline structure preferably employed in a magnetic recording medium such as a hard disk (HD), for example. In particular, the invention relates to a layered polycrystalline structure comprising a seed crystal layer containing non-magnetic atoms, and a magnetic crystal layer containing non-magnetic atoms diffusing along the grain boundaries growing based on the seed crystal layer, and to a method of making the same.
2. Description of the Prior Art
A magnetic polycrystalline film is generally employed in a magnetic recording medium. The magnetic polycrystalline film includes Cr seed crystal layers formed over the front and rear surfaces of a disk substrate, and Co-based alloy layers or magnetic crystal layers formed based on the epitaxy from the respective Cr seed crystal layers. Non-magnetic atoms such as Cr atoms contained in the Cr seed crystal layer are allowed to diffuse along the grain boundaries of the crystal grains formed within the Co-based alloy layer. The diffusion of the Cr atoms enables reduction in the magnetic interaction between the adjacent magnetic crystal grains. The magnetic polycrystalline film of this type enables a reliable reproduction of a magnetic information data without noise.
When the epitaxial Co-based alloy layer on the Cr seed layer is subjected to heat treatment, the Cr atoms are allowed to diffuse along the grain boundaries in the aforementioned manner. At the same time, the Cr atoms are also allowed to diffuse into the lattices of the crystals in the Co-based alloy layer from the Cr seed layer off the grain boundaries. An incomplete non-magnetic region may be established within the Co-based alloy layer along the boundary to the Cr seed layer. Such an incomplete non-magnetic region is supposed to generate noise in reproduction of a magnetic information data.
As generally known, the minimization of magnetic crystal grains within the Co-based alloy layer leads to reduction in noise in reproduction of a magnetic information data. In the case where the Co-based alloy layer is allowed to epitaxially grow on the Cr seed layer, it is impossible to achieve the minimization of the magnetic crystal grains within the Co-based alloy layer unless the crystal grains can be minimized within the Cr seed layer. No specific means are heretofore proposed to simultaneously achieve the minimization of the crystal grains within the Cr seed layer as well as the sufficient diffusion of the Cr atoms along the grain boundaries.